81 CB750c looks like its not charging the battery when lights are on

Pwnypower

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Hey all!

I finally got a new battery for my cb750c. One with a digital display that lets me know when the battery is getting low by beeping or flashing the display.

I just put it in my bike and went for a ride. I started a couple of times and went on the ride. When i came back( with lights and everything on) the battery was beeping and was at 12,0V. When i charged it back up and went for a ride without the lights on it didnt beep.

A charging issue perhaps? So i checked the voltage that got to the battery when the bike was idling and on cruising speed(2-3k RPM).

On idle it was 13,8-9V and when cruising it went op to 14,3.

What could be wrong? Because the battery should be charging when around 14,3. What could be bad? The regulator or the charging spools of the stator?

Kind regards, and happy riding!

pwnypower
 

brettp

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If you're at 14V the stator and rotor are good. And your RR is letting the right voltage through. I'd say your battery is dead
 

Pwnypower

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but the battery is just brandnew, is it possible that it charges with too little of amperage and that i need to check the alternator going to the battery?
 

Pwnypower

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i think i found a problem. The charging is not commecing. When idle the battery is 12,6V and staying there.I found this link:

And you need to check the regulator by bypassing it. As when your key is on it should let through about battery voltage on the black/white wires.

When i bypassed the regulator the alternator started charging,whilst being 13V only it still was way more then 0V. I think my regulator needs changing out badly.

any thoughts on this?
 

brettp

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The charging system on these bikes was never strong. The bike does not charge the battery at idle because the charging system does not produce enough current to do so. You have to keep the bike at 3k RPM minimum to produce enough voltage to charge the battery. If you bypass the RR while revving the engine you can kill the battery by over charging it. If you keep the bike at idle and bypass the RR I'm not sure how much difference in voltage you'll read.
You should be concerning yourself with the wire from the RR that goes to the battery (red/white, I believe) and it's connections.
 
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